Monitoring-based spectrum management for expanding opportunities of white space utilization

Spectrum management is one of the key functions needed for opportunistic spectrum access (OSA) to utilize white space without causing harmful interference to incumbent receivers. Geo-location database approaches using radio propagation estimation have been regarded as practical spectrum management methods. However, propagation models inevitably include an estimation error of path loss in actual radio environments, resulting in estimation error of carrier to interference ratio (CIR) of the incumbent receivers. Consequently, an allowable transmit power of the opportunistic system has to be limited to keep the CIR at a required level. This could prevent white space from being efficiently utilized. To improve the accuracy of CIR estimation, we propose monitoring-based spectrum management. In the proposed technology, referred to as Interference Monitoring, a monitoring node located near the incumbent receivers actually measures both the interference signals and the incumbent signals. Using the measurement results, the CIR estimates are compensated based on minimum mean square error (MMSE) criterion. The proposed Interference Monitoring can be extended cooperatively to utilize spatial diversity. Analytical evaluations assuming a simple cellular system model show that the Interference Monitoring can more accurately estimate CIR, and thus it can significantly increase the allowable transmit power. For an urban macro cell, the Interference Monitoring with a single node achieved more than a 4 dB increase of the transmit power; the Cooperative Interference Monitoring with 4 nodes achieved more than a 7 dB increase. Thus, the Interference Monitoring can expand opportunities for white space utilization without increasing the interference to the incumbent system.